Understanding hydraulics and cylinder drift

[OCR]

Good find, pajibson... :thumbsup

Here's some more from HydraulicSupermarket.com...

I posted some of this years ago; I suppose it's in the Archives by now... lol

Anyway, there's some good reading... :cool2

Hydraulic technical library:

http://www.hydraulicsupermarket.com/technical.html

Hydraulic product library:

http://www.hydraulicsupermarket.com/products.html

Brendan Casey's blog:

http://www.hydraulicsupermarket.com/blog/


Really, bookmark it, and reference it every now and then... :yup




OCR

 

[neilhans]

Its a really a great post. learned many things about hydraulic cylinder and drifts and learned about structures of their. Operations also help me out in better ay to understand more deeply about them.

 

[JANAOHIO]

I don't understand why a bobcat roll cylinder is possible to drift but a crane or excavator doesn't. is it because of weight ??? because a excavator bucket has weight also as well as the boom

 

[dosr911]

Read this article and there is alot of great information, being that I am really green when it comes to hydraulics. hopefully someone can give me some insight being that I'm a rookie:/ I have an aerial forklift with parallel hydraulic cylinders (jlg skytrak) I had the cylinder taken in due to the cylinder leak, no testing was done just took it in (rookie move I know) so I get the cylinder back put it in and I am able to lift the cylinder but it doesn't want to go down. I can hear the machine trying to pull it down but won't go, at times it will retract but really slow. I have checked my lines, all seems well. Sometimes I will get a slight whistle pull i'll then pull lever after the whistle it goes down just fine. Air In Cylinder? Relief valve? Cylinder by passing? Tia

 

[theironoracle]

Tia, those cylinders are equiped with a cylinder check valve, this is a safety valve that keeps the boom from dropping if there is a failure in the boom up curcuit like a blown hose. The valve only opens when the pressure on the down hose opens it and allows return oil to flow. It is screwed into the block at the base of the cylinder replace it and see what happens. TIO

 

[dosr911]

Tia, those cylinders are equiped with a cylinder check valve, this is a safety valve that keeps the boom from dropping if there is a failure in the boom up curcuit like a blown hose. The valve only opens when the pressure on the down hose opens it and allows return oil to flow. It is screwed into the block at the base of the cylinder replace it and see what happens. TIO

Thank you theironoracle, I will give it a shot, thanks for your input

 

[willie59]

Thank you theironoracle, I will give it a shot, thanks for your input

Be very careful removing that holding valve on the boom hoist cylinders. Make sure the boom is fully at rest, not in the air, and even then, when you remove that valve cartridge there may be some residual pressure, just be very slow and careful removing it.

 

[dosr911]

Be very careful removing that holding valve on the boom hoist cylinders. Make sure the boom is fully at rest, not in the air, and even then, when you remove that valve cartridge there may be some residual pressure, just be very slow and careful removing it.

Thank you willie I will.

 

[dosr911]

Update, I replaced the valve and all is ok! Thanks again fellas, really appreciate it! What might of caused this valve to fail? Wear and tear?

 

[lantraxco]

If it was fine before you took the cylinder in, and not working correctly after, it's most likely got some contaminant stuck in it, part of a seal or a metal shaving from inside the cylinder, or possibly some dirt that got into the lines when you removed or replaced the hoses. Just guessing.

 

[willie59]

If it was fine before you took the cylinder in, and not working correctly after, it's most likely got some contaminant stuck in it, part of a seal or a metal shaving from inside the cylinder, or possibly some dirt that got into the lines when you removed or replaced the hoses. Just guessing.

Yep, it doesn't take much of a fragment to foul up a holding valve cartridge.

 

[dosr911]

Makes sense it would be garbage. Missed quite a bit of garbage when I pressure washed it, doesn't help that it's spends most it's life on a dairy. Next time ill make sure i get all that crud off before disconnecting lines.
But now the boss is happy happy happy

 

[Toms78case]

I can relate to this thread. Yes I know this is not a tractor, but. Some of the aerial knuckle booms where I was working at a few years ago used in the matching elbow cylinders, a fixed holding valve on one cylinder and an adjustable holding valve on the other cylinder. We would sometimes have to adjust the adjustable side so the boom tip did not move sideways when movement started in the up or down direction. When the adjustable valve closely match the fixed the boom tip would move straight up and down when the function was moved.

We used a holding valve that allowed 5 drips per minute on most of our cylinders. there is a german manufactured holding valve that has a positive close and is made with "O" rings to stop even that drift rate.

Back on the drifting of cylinders. Heat is one thing that was not mentioned. While it is more pronounced on a cylinder that is 288" long, during operation with normal temp hydraulic oil introduced into that cylinder, I have seen them cool after being raised and move down as much as 3" inches as well as that same cylinder in cool weather after raised during operation. Enter the warm sun out from behind the clouds warming the cyl and it expands (raising) the boom extension.

Sorry just another perspective on that.

Another Tom V. IFPA MHM AJPP

 

[ctheddy]

So I've got a bobcat 442 with significant boom drift. Haven't had much time to pin point the issue, but if I understand correctly it shouldn't drift because it is putting down-pressure on the piston side and also the holding valve on the cylinder should "hold" the load? The ram seal seems good so I'm guessing my holding valve is shot? Also if the holding valve isint functioning correctly, the control valve should still hold the load with minimal drift, so I probably have boom control valve issues also?

Great thread, very informative! Thanks for your insight